Spiral stair units are of convenience when access is needed between two floor levels but there is insufficient space for conventional stairs using either straight runs of treads (and risers) or a combination of shorter straight runs plus an intermediate landing(s). Further, spiral stair units are often utilized to provide an interesting interior design when there is needed access between two levels. While such spiral units can be utilized in industrial applications (usually all-metal structures), the present invention is more applicable to residential applications and is generally of wood construction.
Spiral stair units, as well as circular stair units, are most often constructed using lamination techniques to construct handrails (also called banisters) for the support of stair treads. This permits the preforming of the spiral configuration of these elements. Such fabrication must be accomplished in a factory remote from the site of use of the finished product. Further, these elements are usually joined at the factory using the multiplicity of spindles or balusters and the stair treads joining a central support and, in some constructions, to a preformed stringer (as for a circular stair unit). Each stairway unit is essentially custom built since the total spacing between floor levels may vary as well as the size and number of treads. The entire unit then must be shipped to, and installed at, the ultimate site of use. This is a rather cumbersome effort of shipping and installation.
There are some spiral (and circular) stair units that can be fabricated on-site, thereby reducing the problem of shipping of a large object. One such unit is that described in U.S. Pat. No. 3,418,770 issued to T. Allmand on Dec. 31, 1968. The stair unit of that patent has stair treads cantilevered from a central post, upright balusters, and a segmented handrail. Each segment of the handrail is a solid bar, and mechanical connection is made between ends of each segment.
Another spiral staircase that can be constructed on-site is that described in U.S. Pat. No. 3,491,498 issued to W. Hughes on Jan. 27, 1970. This unit utilizes a segmented and spiral central support from which stair treads are cantilevered. The central support is made up of segments, one each for between a pair of stair treads. Tensionable cables thread through these central support segments, and the stair treads, which strengthen the structure when tensioned.
U.S. Pat. No. 4,869,034 describes a sectional circular staircase. In this construction, both the stringers (outside and inside), as well as the banisters, are made up of a plurality of blocks strung together with cables. The blocks of the banisters and stringers are mitered in two directions at both ends to permit a pre-determined formation of the banisters. The cables, when tensioned, provide stiffness to the respective portions of the stairs. Spaced horizontal treads join the inside and outside stringers in this design. This design permits the construction of the circular stair unit on-site. However, the construction does not lend itself to the fabrication of a spiral stairway. In addition, each component of the unit must be custom-designed to achieve a selected total height, tread width and angle of the turn of the circular stairway.
Accordingly, it is an object of the present invention to provide a stairset which can be easily assembled into a spiral stairway on site from substantially "off-the-shelf" prefabricated components so as to achieve convenience in shipping and movement at the site, and yet permit off-site fabrication if desired.
Another object of the present invention is to provide a stairset wherein components forming a banister are a multiplicity of substantially standard and preformed segments threaded by a cable, the cable having means for post-tensioning, with distal ends of stair treads being joined to the banister with at least one baluster.
A further object of the present invention is to further provide a stairset for a spiral stairway wherein proximal ends of stair tread units are separated by spacers in a central column of the spiral, and distal ends are each separated from each other with braces to provide proper and rigid support of the distal ends, the spacers and braces providing for the riser height of the stair tread units for a selected spiral stairway.
It is also an object of the present invention to provide a method for readily assembling a spiral stairway on- or off-site using a stairset having a banister fabricated from a plurality of segments threaded by a cable whereby post-tensioning of the cable provides rigidity to the banister, and distal ends of stair treads extending from a central support are joined to the banister with at least one baluster.
Also, it is an object of the present invention to provide a stairset for a spiral stairway, and a method for assembly, that utilizes a segmented banister wherein there are a selected whole number of segments for each stair tread unit, with a post-tensioned cable threading all segments of the banister to give rigidity to the banister, with there being one baluster attached between each banister segment and a distal end of respective stair treads units whereby the same number of balusters as banister segments connect to each stair tread unit.
Another object of the present invention is to provide a stairset, and method of assembly, that creates a spiral stairway having a unique and aesthetically-pleasing appearance.
These and other objects of the present invention will become apparent upon a consideration of the drawings referenced below together with a complete description thereof.